博士 / 國立臺灣大學 / 造船及海洋工程學研究所 / 88 / The tidal characteristics are investigated through the harmonic analyses of tidal data around the coast of Taiwan and along the coast of China inside the East-Asia Continental shelf. The topography is established according to the sea charts published by the Naval Hydrographic Office, Taiwan. Based on the anomalous amplification of the semidiurnal constituents that derived directly from data survey, the theories of co-oscillating tides are adopted to verify the effects of the shelf. A frequency-domain mild-slope equation in rotating fluids (Tsay, 1991) is re-derived. Numerically, a depth-integrated two-dimension hydrodynamic model, which developed by Danish Hydraulic Institute (DHI), is applied to investigate the propagating mechanics of tidal wave as well as the dynamical characteristics of tidal currents. Furthermore, a finite element computational model, which based on the frequency-domain mild-slope equation, is implemented to identify the co-oscillating mechanisms induced by the semidiurnal constituents.
The measurements of tides reveal that the tidal characteristics are influenced by the topography. The shelf length of 650 km obviously affects the tidal co-oscillating characteristics in Taiwan Strait. Maximum tidal ranges and small time differences of high water appear near the intermediate section of the shelf, however, minimum tidal ranges associated with significant time differences are observed both on shelf ends. Nearly symmetrical appearances both of tidal ranges and time differences of high water appear on the shelf. Applying the co-oscillating theories to analysis the peculiar appearances, a partially standing wave existing over the shelf is verified. The nodes and anti-node of the partially standing wave thus demonstrate the peculiar appearances both in space and time domain. Moreover, due to the averaged water depth near 80 m in the strait, the semidiurnal constituents with half of the wavelength, 600 km, which approximately equal to the shelf length, will satisfy a co-oscillating resonant condition. This implies that the semidiurnal constituents mainly induce the peculiar appearances of tidal ranges with mechanism of co-oscillating resonance in the Taiwan Strait.
From the computational results of the two-dimension hydrodynamic model, it is observed that the propagating direction of tidal waves is obviously unitary from north to south in the strait. Significant inconsistencies with the traditional common sense are found. However, it is true by relating to the appearance of the partially standing wave. Due to the semidiurnal constituents mainly appeared as the partially standing wave, therefore, the propagation direction is dominated by the diurnal constituents, which has been verified to propagate in direction from north to south in the strait by using finite element model. Furthermore, the tidal currents are also closely related to the partially standing wave, in particular, the variations of magnitude of tidal currents as well as current directions strongly depend on the tidal elevations at station of Taichung (TC). It is observed that currents are inflow from both ends to the central part of the strait during the flooding period at station TC, and are outflow to the adjacent ocean during the ebbing period. The corresponding current elliptic is counterclockwise sense at the north end, and is clockwise sense at the south end of the Taiwan Strait.
A finite element mode with local radiation boundary condition (Chen & Tsay, 1990), which based on the frequency-domain mild-slope equation in rotating fluids (present study; Tsay, 1991), is applied to investigate the tidal characteristics appeared by the major constituents. It is found that the scattering waves can well be regulated on the open-sea artificial boundary by implementing the local radiation boundary condition, even though the computational domain is not large enough to satisfy with the thumb rule of one times of the wave length. With the Coriolis effects neglected, the mild-slope equation (Berkhoff, 1972; Smith & Sprinks, 1975) is successfully extended to compute the tidal wave. With the Coriolis effects included, a partially standing wave, which demonstrated evidently by the semidiurnal constituents, is further identified existing in the Taiwan Strait. From the co-range charts associated with the equi-phase charts of semidiurnal constituents, it is easily to identify that the partially standing wave with its anti-node appears right at intermediate section of the strait, and its notes locates right outside the coast of stations Keelung and Kaohsiung, respectively. The distance between these nodes are approximately equal to the shelf length. This justifies furthermore that the nodes locate right near to both of the north and south entrances of the slender strait. On the other hand, based on the amplification response curve, the characteristic period of resonance is found between 13.2 and 14.0 hrs. Due to most of the periods of semidiurnal constituents are approximately near the band of resonance, therefore, resonance of semidiurnal constituents are identified occurring in the Taiwan Strait, of which the shelf topography, the water depth over the shelf, the geometry and aspect ratio of the slender strait play very important roles.
| Identifer | oai:union.ndltd.org:TW/088NTU00345033 |
| Date | January 2000 |
| Creators | Wen-Jye Juang, 莊文傑 |
| Contributors | Ming-Chung Lin, 林 銘 崇 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 284 |
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